All sirens were completely shut off by 1:20 a.m. City officials said that Dallas 911 received 800 calls during a fifteen minute period around midnight.
WFAA viewers began reporting the sirens at around 11:44 p.m. Friday.
Outdoor emergency warning sirens went off across Dallas late Friday, despite no severe weather or any other live emergency threat.
City spokeswoman Sana Syed said Saturday that hacking is one of the possible causes investigators are considering.
Dallas officials said they are collaborating with the Federal Emergency Management Agency to create a wireless alert system that would circulate messages to every cell phone in the area in the event of a real emergency.
City leaders said they did not know how the hacker gained entry, but said they are investigating the matter.
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Vaz said he expects the emergency siren system to be back in operation by Monday afternoon.
Officials say fire dispatch crews had to manually shut off the sirens.
Many people, naturally, found the sirens unsettling and some took to Twitter to post video of the incident while the city collectively wondered what impending doom the sirens might be warning of. "We had no malfunction".
The city's top priority is to work on reactivating the system.
Dallas Mayor Mike Rawlings promised the perpetrator would be found and prosecuted. "We ask residents to be patient with us in case the sirens sound again during re-activation and please do not call 911 or 311 for concerns about sirens", the city said in a news release.
The city also reminded residents that they may hear sirens again as engineers determine if the system is functioning properly.